How can marketers create persistent, continuous forms of engagement with customers?

I agree with Eric, but would add that the "series of regular, small engagements" will be more engaging if they build a story over time, rather than serve as one-off nuggets on a variety of topics.

The point made about shorter content is a good one. Think about it this way - if you were multi-tasking (which you probably are) can you actually read your content, get a takeaway that matters while quickly switching gears?

The language we use must also be designed for rapid uptake. Get rid of the professorial words and jargon and have a conversation. You can still provide meaty content without the hyperbole - and your audience will like you for lessening their effort to engage with you. They'll really, really like you :)

Actually talk with them from time to time rather than simply firing content at them.

Being on multiple channels and being ready to interact and participate in the discussion which your content hopefully generates is key too.

I was at a family event over the weekend and I asked a few people about online channels and if they really thought about them when they used them. The response was that it's intuitive for them, they really don't think about what channel they are on and just move between them as the (practicality) conversation suits.

Admittedly, that's anecdotal evidence, but I thought I would share it just the same.

Regards,
Jim